A conventional wiper control apparatus includes a rain detection device for detecting raindrops on a windshield glass in order to automatically control a wiper in accordance with a state of rainfall. It also includes a wiper driving device having a controller to which an external signal such as a signal of a wiper switch is input (for instance JP-A-2001-99948).
In this wiper control apparatus, the rain detection device includes a pair of a light-emitting element and a light-receiving element for optically detecting raindrops on the windshield glass. The rain detection device also includes a control circuit that makes the light-emitting element emit light when the raindrops are to be detected. The control circuit selects a wiping speed or a wiping mode of the wiper in accordance with the detected amount of raindrops and outputs a wiper driving signal in accordance with the selected wiping speed or wiping mode to the controller in the wiper driving device. Moreover, vehicle information such as a switching signal of the wiper switch for determining whether to perform rain detection or not and a driving position signal for the wiper, is input to the controller. This vehicle information is output from the wiper driving device to the rain detection device.
The control circuit in the rain detection device and the controller in the wiper driving device are provided with respective communication circuits for bidirectional communication.
In order for the rain detection device to detect the amount of raindrops, it is necessary to send the vehicle information such as the driving position signal for the wiper to the rain detection device. The sending of the vehicle information is performed by the communication circuit of the controller of the wiper driving device. On the other hand, it is necessary to send the wiper driving signal from the rain detection device to the wiper driving device. The sending of the wiper driving signal is performed by the communication circuit of the control circuit of the rain detection device. Thus, a plurality of communication lines is usually connected between the communication circuits of the control circuit and the controller for bidirectional communication, thus making the communication system complicated.